Call hook_civicrm_selectWhereClause from the BAOs

As of today the hook_civicrm_selectWhereClause is only called from the API. It needs to be called from the BAOs, the CRM_Report_Form class and most probably the CRM_Utils_Sql_Select class.

This issue is only related to implementing the hook in the BAOs. Other implementation will be listed in additional tickets.

Calling this hook consistently will enable the re-implementation of several pieces of code that now live in core through extensions - Multisite, Financial ACLs and eventually ACLs. The last two would be 'core extensions' packaged and shipped with core.

For multisite, priority BAO are: Membership_Type, Event, Contribution_Page and Payment Processor. We can then extend (if relevant) to the lower-level 'utility' and 'settings' tables (Menu, Navigation, Job, Option_Value, Mail_Settings, Word_Replacement, etc).